IMPROVE EQUIPMENT
After you have improved your insulation and windows to reduce your heating and cooling needs, the next step is to invest in more efficient HVAC equipment. Different types of HVAC systems are rated using different methods by different authorities.
Gas heating is typically rated in terms of percent efficiency, meaning how much energy comes in versus how much heat is output. Today, most gas-heating equipment is 80 percent efficient. Older systems—those more than 20-years old–are often 65 percent efficient or less. High-efficient furnaces, boilers and heaters are often 88 to 95 percent efficient.
After you have improved your insulation and windows to reduce your heating and cooling needs, the next step is to invest in more efficient HVAC equipment. Different types of HVAC systems are rated using different methods by different authorities.
Electric equipment is always rated by coefficient of performance, or COP, with electric resistance heat being equal to 1.0. Air- or water-source heat pumps are typically 3.5 COP (+/- 1.5 COP depending on many factors, such as heat sink/source, compressor technology and outdoor temperature.), which means they are three and half times more efficient than electric-resistance heat.
Air conditioners are rated many different ways, often depending on the size and type of equipment. Residential A/C units are rated in seasonal energy efficiency ratio, or SEER. The legal minimum set by U.S. law and regulated by the U.S. Department of Energy is now 13 SEER. Most older units—those more than 20-years old–are 6 to 10 SEER. The best residential units on the market today are 19 to 21 SEER.
Commercial A/C equipment is rated in energy-efficiency ratio, or EER, and 9.5 to 13 EER is common. Unlike the residential marketplace, EER is set by building codes at the local level and enforced by the authority-having jurisdiction, so there will be different minimum EERs depending on location and sizes of equipment. For smaller equipment, 15.2 EER is the best on the market today. Larger equipment, such as chillers are rated in kW/ton Integrated Part Load Value. Air-cooled machines are typically 1.2 kW/ton or lower, and water-cooled machines are often 0.72 or lower. These are average ratings. For air-cooled systems 1.04 is more efficient, and 0.33 is best for water-cooled systems.
Enhance Operations
Tight buildings are great, as is highly efficient equipment, but how you operate your HVAC system is most important. There are dozens of examples of things that can be done to operate your existing system using less energy without sacrificing comfort. The basic premise is: Do not use more energy than you absolutely must.
Implement setback schedules in your controls system to automatically change the heating and cooling settings when the building is not in use. Bring in only the code-required amount of outside air. Use waste exhaust air to pre-heat or -cool the ventilation air. Much can be done very inexpensively to improve your equipment’s efficiency–sometimes with the equipment and controls you already own.